The present invention relates to a heat-insulated flexible pipe used for example for carrying effluents produced by oilwells, or for shipping or land carriage of liquid requiring thermal insulation.
The problem of thermal insulation of subsea petroleum production pipes arises in particular for reservoirs whose effluents, subjected to fast cooling due to the sea bottom temperature and to the thickness of the water depth, undergo physico-chemical phenomena that disturb their flow in the pipe. Hydrate formation, paraffin, asphaltene deposition or oil gelation may notably occur.
The term flexible pipes refers here to pipes consisting of polymer layers and metal reinforcing armours, and also to wound, then unwound metal tubes. In fact, the problem of thermal insulation is the same for both types of pipe: the thickness of the insulating material must not stiffen the pipe so that it can be used in the same way as a pipe without an insulant. In other words, the xe2x80x9cflexibilityxe2x80x9d or the xe2x80x9crigidityxe2x80x9d of the pipe must be substantially identical, with or without an insulant.
Document EP-4,006,689 describes a flexible pipe thermally insulated by helical winding of strips made of expanded plastic. These relatively thin strips are wound by elastic deformation around the core of the flexible pipe. The insulating material selected should therefore allow implementation of this winding operation, which is furthermore quite extensive since several layers are necessary, while having a sufficient characteristic as regards heat insulation and mechanical strength under difficult hydrostatic pressure conditions. However, this solution is not appropriate with a high outside pressure because the wound strips do not withstand high compressive stresses.
Rigid plastic materials are well-suited for insulation and mechanical strength, but stiffening of the pipe is problematic with great thicknesses.
The present invention thus relates to a method intended for heat insulation of a flexible pipe according to the definition given here, comprising the following successive stages:
depositing, on the outer surface of the pipe moving longitudinally, a thickness of extrudable and rigid insulating material,
cooling the insulating material over a substantially rectilinear part downstream from the deposition area,
forming at least one circumferential slot in said thickness of the material in relation to the axis of the pipe so as to restore the flexibility of the pipe once coated with the rigid insulating material.
In a first variant, the slot can be made by machining.
In a second variant, the slot can be made as the material is deposited on the pipe.
According to the invention, the slot can be helical, with a determined width and pitch according to the allowable bending radius of the flexible pipe.
In a variant, the slot can consist of a succession of circular slots having a determined width and pitch according to the allowable bending radius of the flexible pipe. The term pitch refers here to the distance between two slots on a generatrix of the pipe.
An extruding head can be concentric to the pipe.
In a variant, an extruding head can be arranged laterally to the pipe and revolve in relation to the pipe so as to deposit said material in the form of a helical strip.
Extrusion can be performed in several successive layers so as to reach great insulant thicknesses.
A layer of sticking preventive material, for example an antiadhesive strip coating, or grease or equivalent, can be deposited on the outside of each layer of extruded material.
In the case where the operation is carried out with several layers, each layer can comprise machined slots.
The invention also relates to a heat-insulated flexible pipe comprising at least one layer of rigid and extruded insulating material on the outside of said pipe. The layer comprises means for restoring the flexibility of the insulated pipe in the form of at least one circumferential slot.
In the pipe, the width and the pitch of the slots can be calculated according to the allowable bending radius of the pipe.
In the pipe, the slot can be filled with a material that can flow, such as a gel or grease.